lagging window buildup

Hi,

I have just linked a very small systray application under Windoze XP 64 with Eclipse and MinGW. The small app has only basic impelemtations of QSystemTrayIcon functionality (minimzing to tray and maximizing to normal). The app itself works fine. The problem is, that the window buildup lags when minimizing to tray and back to normal view.
Lags only appear when the app was linked with MinGW. The same code compiled and linked with Visual Studio or Eclipse CDT under Linux, there are no lags.

What could be the problem? MinGW is foobar?

thx